Formula for reducing by a specific amount

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I am trying to figure out how to calculate a sum reducing by a specific amount...i.e. I have 100 lots to pay HOA dues on @ $120 per quarter. I am budgeting to sell 3 homes per quarter so want to reduce this amount by 3 each time and figure out what my final number will be when all 100 lots are sold. Is there a way to do this? I am thinking an amortization schedule but I can get it to work. I can't do a nested if function because there are too many conditions. Any ideas??

Hi there,

Not totally sure if this is what you're after, but it's a quick'n'dirty of what I think you're looking for.